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Go Dawgs · 03-24-2011, 10:59 AM

I have an 87 Allergo Bay 33'.

For the most part it is in great condition for its age. I have a few things to fix and or remodel.

My gas gauge is stuck on F and I know the tank is not full. I also know it was not full when I picked it up. What is causing this?

Thanks

Paul R. Haller · 03-24-2011, 11:26 AM

Most fuel tank sender modules are simply a resistance coil depending on fuel level. If the lead wire shorts out to the chassis, the gauge will always read full. Find the lead wire and remove it from the gauge... it should read empty. You have to figure out if its the wire that's shorted, the sending unit that's gone bad, or the gauge.
-Paul R. Haller-

bigskymt · 03-24-2011, 11:30 AM

An "F" reading on a Chev chassis usually indicates an open between the guage and sending unit.................like a broken wire. You can trace the wire from the sending unit forward. On most older P-30s the wire harness ran near the starter where it was subject to manifold heat.
An "E" usually indicates that same sending unit wire is shorted to ground. If you have other then a Chevy I'm not sure.
Having worked for Chevrolet for many years I have to disagree with Mr. Haller's diagnosis, sorry.

Go Dawgs · 03-24-2011, 11:56 AM

Thanks for the replies. I thought it might be either at the gauge or the tank. I will check both areas tonight when I get home.

JimM68 · 03-24-2011, 01:03 PM

Quote:

Originally Posted by bigskymt

An "F" reading on a Chev chassis usually indicates an open between the guage and sending unit.................like a broken wire. You can trace the wire from the sending unit forward. On most older P-30s the wire harness ran near the starter where it was subject to manifold heat.
An "E" usually indicates that same sending unit wire is shorted to ground. If you have other then a Chevy I'm not sure.
Having worked for Chevrolet for many years I have to disagree with Mr. Haller's diagnosis, sorry.

I'm with him. you have an open circuit between the gauge and the sending unit. Start at the top of the gas tank and look for wires that fell off. Most have a separate ground wire from the tank sending unit to the chassis as well, that breaks or comes off, guage reads full.

Midniteoyl · 03-24-2011, 02:15 PM

So, if an 'open' shows as 'full', then with the key 'off', the gauge should show 'full'... correct? 'Cause if it shows 'empty', you guys have it backwards.

Go Dawgs · 03-24-2011, 02:37 PM

Yes it stays on full whether the key is on or off

Mike Canter · 03-24-2011, 03:18 PM

If you find the wires attached are tight to the sender on the tank then take them off and see what the gauge reads then short them together and see what the gauge reads. If the gauge moves then the gauge is good and the wires to the gauge are good and it is a good indication that the sender is bad. Some senders are a floating ring then go up aine down two guids or thin wires. It is possible that the floating ring is stuck at the top of teh guides.

ga traveler · 03-24-2011, 05:13 PM

Sorry midniteoyl you have got it wrong. Remember when you turn off the switch, you removed power to the gauge. So the guage goes to zero, because the power is gone.

Midniteoyl · 03-24-2011, 08:57 PM

Um... if an 'open' shows 'full' then that means it takes power to move the gauge from full because an 'open' circuit has no power...

See what I mean?

The fuel gauge is basically just a volt meter. Usually the gauge reads empty with no power applied... as in an open.

Devil Dog · 03-24-2011, 11:50 PM

I had several fuel gauges stick on full over the years on pickup trucks when I filled them too full. After using some of the fuel I smacked the dash and freed them right up! That would be too easy though.

ga traveler · 03-25-2011, 07:32 AM

Midniteoyl if you look in the light duty truck service manual from chevy. PN ST330-81. On page 8c-5 item 1 disconnected or loose ground wire ,at tank will cause tank to read full.

Midniteoyl · 03-25-2011, 12:11 PM

Quote:

Originally Posted by ga traveler

Midniteoyl if you look in the light duty truck service manual from chevy. PN ST330-81. On page 8c-5 item 1 disconnected or loose ground wire ,at tank will cause tank to read full.

Weird.. will take your word for it though.

Go Dawgs · 03-25-2011, 08:35 PM

OK. I have looked behind the dash, in the engine compartment, and on the starter and no loose wires. I can't get to the top of the gas tank without dropping the tank. There is insulation all on the underside of the MH. I think I may take it up to the gas station and fill the tank and see if the float is just stuck. Any other ideas???

Thanks
Arnold